It is well known that an increasingly important consideration in the production and use of integrated circuits (ICs) is the package in which the IC resides. The module or casing in which the IC is packaged is an important factor in the ultimate cost, performance and lifetime of the IC. For example, as ICs become more dense, dissipation of the thermal energy generated by them in an efficient manner becomes increasingly important in permitting their useful life to be as long as possible. Another consideration as the circuits become denser is that the number of leads to the package and connections from the leads to the integrated circuit pads increases; thus increasing the complexity of construction and adding to the cost of the end product, not just in terms of increased and more expensive materials, but also increased production costs. These considerations are aggravated with the requirements of power circuits, that is, those circuits which handle relatively large amounts of power. For example, higher speed "BiCMOS" memory devices are driving to higher power consumption--in excess of 0.8 W--relatively high for an integrated circuit. BiCMOS is an acronym standing for integrated circuits using both bipolar and complementary metal oxide semiconductor technology. Small outline, J-lead (SOJ)-type packages have lower inductance advantages, but because the package is smaller, the thermal energy dissipation capability is lower.
Another factor affecting the design of IC packages is the advent of surface mount technology, whereby space is conserved on the printed circuit boards (PCBs) by mounting the packages directly on the conductive patterns of the circuit board, rather than by extending the leads through holes in the board. This technology is an additional influence in making the packages smaller, and making it more difficult to design a small package that will dissipate thermal energy readily.
Thus, a continuing goal in the art of providing packages for electronic components such as integrated circuits is a package design that will address these multiple goals satisfactorily in an arrangement that can be reliably manufactured at the lowest cost. The lowest cost packages are those which have plastic bodies which can be molded from thermoplastic and thermoset materials. However, a difficulty in molding plastic packages containing heat sinks is that excess mold material or "flash" creeps around the heat sink. Obviously, at least one surface of the heat sink should remain exposed to provide the surface area for maximum heat transfer to the ambient. The presence of mold flash over this surface inhibits the desired heat transfer. Removing the mold flash from this face of the package can be time-consuming and difficult.